12 GENERAL MORPHOLOGY AND BIOLOGY 



If the cells divide only in one axis, and through the consistency 

 of their envelopes remain attached, then a chain of cocci will be 

 formed. A species in which this occurs is known as a strepto- 

 coccus. If division takes place irregularly the resultant mass may 

 be compared to a bunch of grapes, and the species is often called 

 a staphylococcus. Division may take place in two axes at right 

 angles to one another, in which case cocci adherent to each other 

 in packets of four (called tetrads) or sixteen may be found, 

 the former number being the more frequent. To all these forms 

 the word micrococcus is often generally applied. The individuals 

 in a growth of mfcrbcocci often- show a tendency to remain 

 united in twos. These are spoken of as diplococci, but this is 

 not a distinctive character, since every coccus as a result of 

 division becomes a diplococcus, though in some species the 

 tendency to remain in pairs is well marked. The adhesion of 

 cocci to one another depends on the character of the capsule. 

 Often this has a well-marked outer limit (micrococcus tetragenus), 

 sometimes it is of great extent, its diameter being many times 

 that of the coccus (streptococcus mesenteriodes). ' It is especially 

 among the streptococci and staphylococci that the phenomenon 

 of the formation of arthrospores is said to occur. In none of 

 the cocci have endogenous spores been certainly observed. The 

 number of species of the streptococci and staphylococci probably 

 exceeds 150. Usually included in this group are coccus-like 

 organisms which divide in three axes at right angles to one 

 another. These are usually referred to as sarcinm. If the cells 

 are lying single they are round, but usually they are seen in 

 cubes of eight with the sides which are in contact slightly 

 flattened. Large numbers of such cubes may be lying together. 

 The sarcinae are, as a rule, rather larger than the other members 

 of the group. Most of the cocci are non-motile, but a few motile 

 species possessing flagella have been described. 



2. Bacilli. These consist of long or short cylindrical cells, 

 with rounded or sharply rectangular ends, usually not more than 

 1 //. broad, but varying very greatly in length. They may be 

 motile or non-motile. Where flagella occur, these may be 

 distributed all round the organism, or only at one or both of 

 the poles (pseudomonas). Several species are provided with 

 sharply -marked capsules (b. pneumoniae). In many species 

 endogenous sporulation occurs. The spores may be central or 

 terminal, round, oval, or spindle-shaped. 



Great confusion in nomenclature has arisen in this group in con- 

 sequence of the different artilicial meanings assigned to the essentially 

 synonymous terms bacterium and bacillus. Migula, for instance, applies 



